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March 5, 2015: The AAVSO is requesting observations of the symbiotic nova candidate ASAS J174600-2321.3 during the predicted upcoming eclipse of this system. Observers are asked to begin observing immediately (2015 March 5), and continue observations through the end of July 2015. Both visual and instrumental observations are encouraged; the object was at V=12.28 on 2015 February 6.764 (OCN; S. O'Connor, Bermuda). Filtered, transformed photometry in B, V, and Ic are especially encouraged, with several observations per night required during the ingress and egress phases. The project is being organized by S. Otero, P. Tisserand, K. Bernhard, and S. Hummerich, and is an extension of the research program discussed in Hummerich et al. (2015, AAVSO preprint (=eJAAVSO) #295, in press).

The researchers have provided the following discussion of the project:

"The deeply eclipsing system and likely symbiotic nova ASAS J174600-2321.3

RA: 17 46 00.18 , Dec: -23 21 16.4 (J2000.0)

is going to enter an eclipse in mid-March according to the published elements HJD = 2456142 + 1011.5 x E. The eclipse duration is approximately 115 days.

The system has shown a conspicuous brightening of ~4 magnitudes (V) that started in 1999 and has been in outburst since then. Recent photometry shows the system fluctuating around 12.2 mag (V) as recently as 2014 November 07 (JD 2456969.49068; HMB, J. Hambsch, Mol, Belgium, remotely from Chile). It will go fainter than 16.9 mag (V) at mid-eclipse when the red giant passes in front of the outbursting white dwarf. We might also be seeing semi-regular pulsations from the red giant during eclipse.

As no observations around mid-eclipse exist after the considerable brightening of the primary star, the exact shape of eclipse is open to conjecture. Thus, no times of second or third contact are given below, although there was a pronounced time of totality during the eclipse that has been covered before the onset of activity in the system (compare Fig. 4, JAAVSO preprint (=eJAAVSO) #295).

We encourage visual and CCD observations during the eclipse, preferably multicolour photometry to record the colour changes as the red star starts to dominate the total flux of the system. Observations in V, B and Ic would be very valuable (note, though, that the object will be very faint in B during eclipse). During the ingress and egress phases, several observations per night are advisable. During the remainder of the eclipse, one set of observations per night will be adequate due to the long period of the system. Stacking might be advisable to reach the faint magnitudes during the eclipse.

Observations should start as soon as possible to check on the brightness of the object before the eclipse sets in. Once the event is over, continued photometry with a cadence of one observation per week is encouraged to detect the start of the fading phase of this very slow nova.

Spectroscopic observations near mid-eclipse would be very desirable, too.